The present invention relates to a novel polyvinylamine copolymer having the excellent effect in use in the fields of application of cationic polymers, such as flocculating agent for the treatment of waste water, dehydrating agent for organic sludge, and drainage aid, retention aid, paper strength increasing agent, etc. in papermaking industry. More particularly, the invention relates to a vinylamine copolymer having the structural units represented by the following formulae (I), (II) and (III): ##STR3## (wherein X represents an anion or hydroxyl ion) ##STR4## (wherein R.sup.1 represents hydrogen atom or a methyl group, R.sup.2 represents hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R.sup.3 represents an alkyl group having 1 to 4 carbon atoms or an oxoalkyl group having 4 to 8 carbon atoms), in which the molar fraction of the structural unit (I) is 5 to 85% by mole, the molar fraction of the structural unit (II) is 5 to 85% by mole, and the molar fraction of the structural unit (III) is 90 to 5% by mole, a flocculating agent, a drainage aid and a paper strength increasing agent using such vinylamine copolymer, and a process for producing such vinylamine copolymer.
For the preparation of polyvinylamines, there have been known the methods by Hofmann degradation of polyacrylamides and hydrolysis of poly N-vinylamides. Especially, the method of hydrolysis of a single polymer of N-vinylformamides is an excellent method which is capable of synthesizing high-molecular weight polyvinylamines with high stability. However, the polymers obtained by this hydrolyzing method are very high in hydrophilicity and unsatisfactory in effect as a flocculating agent for dehydration. For solving such disadvantage, a method has been proposed in which, in order to afford hydrophobicity to the produced polyvinylamine, N-vinylformamide and ethylene are copolymerized and the resulting product is hydrolyzed. However, since N-vinylformamide and ethylene are not well copolymerizable with each other and incapable of producing a high-molecular weight copolymer, it was difficult to solve said problem by the copolymer of N-vinylformamide and ethylene. The present inventors had previously proposed a flocculating agent using the basic hydrolyzate of a copolymer of N-vinylformamide and N,N-dialkyl(meth)acrylamide [Japanese Patent Application Laid Open (Kokai) No. 61-118406 (1986)]. However, since this hydrolyzate becomes a tetrapolymer containing carboxyl groups, this product, when used as a flocculating agent for dehydration, was incapable of lowering the water content of dehydrated sludge.
As a result of further studies for providing an excellent flocculating agent for dehydration, it has been found by the present inventors that a polyvinylformamide copolymer which has been partially modified under an acidic condition, that is, a polymer comprising the structural units represented by the following general formulae (I), (II) and (III): ##STR5## (wherein X represents an anion or hydroxyl ion) ##STR6## (wherein R.sup.1 represents hydrogen atom or a methyl group, R.sup.2 represents hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R.sup.3 represents an alkyl group having 1 to 4 carbon atoms or an oxoalkyl group having 4 to 8 carbon atoms), in which the molar fraction of the structural unit (I) is 5 to 85% by mole, the molar fraction of the structural unit (II) is 5 to 85% by mole and the molar fraction of the structural unit (III) is 90 to 5% by mole, is a novel high-molecular weight vinylamine copolymer provided with hydrophobicity, and the present invention has been attained on the basis of this finding.